I would advise you to make a 2" hole to have room for insulation. Drill a hole with a 2" hole saw. I would sleeve it too. Take some thin sheet metal and roll it and stick in the hole first and seal around it. Make the top an inch or two above floor level. Center the pipe in the hole and this will give room to insulate the pipe. Insulation is important.

3/4" or 7/8", and if you are going to insulate the pipe, put it against the subfloor on the bottom and start it again from the top of the subfloor. The subfloor will act as "insulation" where the pipe goes through it.

The subfloor will not act as insulation, it will become a sponge if any kind of moisture exists from a sweating or leaking pipe and it could start growing mold. Mold is bad, it can cause allergies and sickness. Make the hole bigger to allow room for insulation to be properly put on the pipe. Putting a sleeve in the hole like a bigger pipe or some rolled thin metal acts as a guard to keep water from going to the floor below. If you have a flood in a bathroom or kitchen it would help keep excess water from getting into the floor below. If you have it apart now, now is the time to think it through. If you now want the hole bigger, take a square of plywood and glue it down over the hole. Let it dry completely and drill a new hole. This is if you are using hole saws.